Hypertension and cardiovascular disease are serious health problems for many individuals in the industrialized world. Atrial natriuretic peptide (ANP) is an endogenous and potent hypotensive hormone that elicits natriuretic, diuretic, vasorelaxant and antiproliferative effects, important factors in the control of blood pressure and cardiovascular homeostasis. One of the principal loci involved in the regulatory action of ANP is the guanylyl cyclase-linked ANP receptor (GC-A), designated as Npra, whose ANP-binding and guanylyl cyclase activities vary remarkably in different tissues. However, the molecular basis of these activities and the functional expression and regulation of Npra gene are not well understood. To further understand the biological role(s) played by Npra, the transcriptional regulation and function of the Npra gene will be studied using a model system cell line and Npra gene- targeted mutant mouse models in the following specific aims: 1) Demonstrate the transcriptional control of the Npra gene expression by identifying conserved regulatory regions. The focus of this specific aim is to determine the complete nucleotide sequence of murine Npra gene, analyze the structural organization and compare with rat gene sequence to identify the 5'-flanking cis-regulatory elements and determine the function of these elements by transient expression in cultured cells. 2) Identify the biochemical and physiological function(s) of Npra gene by analyzing the consequence of its loss or its tandem duplication in gene-targeted mice having, 0, 1, 2, 3, or 4 copies of the Npra gene. The focus of this specific aim is to determine the impact of the Npra gene-dosage and null mutation on cellular, developmental and physiological responses in mutant mice in vivo and in cultured cells isolated from these mice in vitro. The long-term objective of the research proposal is to elucidate, at the molecular level, the nature and mode of functioning of the Npra gene in as much detail as possible. Progress in the filed of research will significantly strengthen and advance our knowledge of genetic and molecular approaches to evaluate the role of Npra in the control of fluid volume, blood pressure, congestive heart failure and other physiological function(s). The resulting knowledge should yield new therapeutic targets for the treatment of hypertension and prevention of hypertension-related cardiovascular disorders.